Enterovirus D68 (EV-D68; genus Enterovirus, family Picornaviridae) can cause severe respiratory illness, with clinical manifestations that include bronchiolitis, wheezing, and pneumonia, especially in children (Schieble et al., Am. J. Epidemiol. 85:297-310, 1967). Since its discovery in 1962, EV-D68 had been relatively rare until it re-emerged in the mid-2000s; since then it has been associated with clusters and outbreaks of severe respiratory disease worldwide (Ikeda et al., Microbiol. Immunol. 56:139-143, 2012; Imamura et al., Emerg. Infect. Dis. 17:1430-1435, 2011; Kaida et al., Emerg. Infect. Dis. 17:1494-1497, 2011; Linsuwanon et al., PLoS One 12:e35190, 2012; Jacobson et al., Pediatr. Infect. Dis. J. 42:309-312, 2012; Rahamat-Langendoen et al., J. Clin. Virol. 52:103-106, 2011; Tokarz et al., J. Gen. Virol. 93:1952-1958, 2012; Renois et al., J. Clin. Microbiol. 51:640-643, 2013; Todd et al., Virol. J. 10:103, 2013; Xiang et al., Emerg. Infect. Dis. 18:821-814, 2012). Beginning in August 2014, EV-D68 caused an ongoing outbreak of severe lower respiratory tract illness among children in the United States, with over 800 laboratory-confirmed cases in 46 states and the District of Columbia (Midgely et al., MMWR 63:798-799, 2014)